linux-kernel - Re: [PATCH 1/2] ARM: gic: add irq

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Date:	Thu, 29 Sep 2011 18:27:51 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Rob Herring <robherring2@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	marc.zyngier@....com, thomas.abraham@...aro.org,
	jamie@...ieiles.com, b-cousson@...com, shawn.guo@...aro.org
Subject: Re: [PATCH 1/2] ARM: gic: add irq_domain support

On Thu, Sep 29, 2011 at 04:02:44PM -0500, Rob Herring wrote:
> On 09/29/2011 12:15 PM, Grant Likely wrote:
> > On Wed, Sep 28, 2011 at 10:53:55PM -0500, Rob Herring wrote:
> >> From: Rob Herring <rob.herring@...xeda.com>
> >>
> >> Convert the gic interrupt controller to use irq domains in preparation
> >> for device-tree binding and MULTI_IRQ. This allows for translation between
> >> GIC interrupt IDs and Linux irq numbers.
> >>
> >> The meaning of irq_offset has changed. It now is just the number of skipped
> >> GIC interrupt IDs for the controller. It will be 16 for primary GIC and 32
> >> for secondary GICs.
> > 
> > [...]
> > 
> >>  /*
> >> @@ -81,7 +82,7 @@ static inline unsigned int gic_irq(struct irq_data *d)
> >>   */
> >>  static void gic_mask_irq(struct irq_data *d)
> >>  {
> >> -	u32 mask = 1 << (d->irq % 32);
> >> +	u32 mask = 1 << (gic_irq(d) % 32);
> > 
> > This can probably change simply to d->hwirq if irq_offset is
> > eliminated as I describe below.
> > 
> >>  void __init gic_init(unsigned int gic_nr, unsigned int irq_start,
> >>  	void __iomem *dist_base, void __iomem *cpu_base)
> >>  {
> >>  	struct gic_chip_data *gic;
> >> +	struct irq_domain *domain;
> >> +	int gic_irqs;
> >>  
> >>  	BUG_ON(gic_nr >= MAX_GIC_NR);
> >>  
> >>  	gic = &gic_data[gic_nr];
> >> +	domain = &gic->domain;
> >>  	gic->dist_base = dist_base;
> >>  	gic->cpu_base = cpu_base;
> >> -	gic->irq_offset = (irq_start - 1) & ~31;
> >>  
> >> -	if (gic_nr == 0)
> >> +	/*
> >> +	 * For primary GICs, skip over SGIs.
> >> +	 * For secondary GICs, skip over PPIs, too.
> >> +	 */
> >> +	if (gic_nr == 0) {
> >>  		gic_cpu_base_addr = cpu_base;
> >> +		gic->irq_offset = 16;
> >> +		irq_start = (irq_start & ~31) + 16;
> > 
> > With the switch to irq_domain, there should no longer be any need for
> > a ~31 mask on the irq_start number.  Yes, you'll want to make sure
> > that it doesn't allocate below irq 16, but the driver should
> > completely use the irq_domain to manage the mapping from linux-irq
> > number to hwirq number.  The ~31 mask appears to have been an
> > optimization to quickly calculate hwirq number from the linux one, but
> > that value is now found in irq_data->hwirq.
> 
> I started out exactly this way removing irq_offset. The problem is the
> core irq domain code assumes that hwirq starts at 0, but for the gic it
> starts at 16 or 32.
> 
> It could be fixed in the domain core, but that would effectively mean
> moving irq_offset into the core.

Fix irq_domain.  If it cannot handle this trivial case, then it won't
be able to handle the complex powerpc use cases.

g.
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